The invention relates to a circuit arrangement for improving the quality of video signals read out from a storage medium by isolating a radio-frequency component, which is conditioned in a signal processing branch parallel to the main signal branch by using a coring stage for suppressing signal components with signal values lying below a first threshold value and which is added to the delayed video signal of the main signal branch.
It is known that the picture quality of conventional VHS and S-VHS recorders is inferior to that of normal video signals. This applies in particular with regard to picture details which are of significance in particular in the luminance signals.
It is known that the picture quality can be improved by establishing a correlation between neighboring signal values (pixels). In principle, this involves conditioning a radio-frequency component of the video signal, for example, of the luminance signal, in a signal processing branch parallel to the main signal branch by limiting and weighting, and then adding it again to the delayed video signal in the main signal branch. One method known to accomplish picture quality enhancement is to divide the luminance signal over two parallel processing branches, a low-pass filter being arranged in one processing branch and a band-pass filter for radio-frequency signal components being arranged in the other processing branch. The band-pass filter is followed downstream by an amplifier and a threshold stage, by which the radio-frequency signal components which are allowed through by the band-pass filter of which the amplitudes below the threshold switching are suppressed. The signal is "decored" of the low amplitude values (coring technique), as a result of which a noise reduction is attained. The signal components of the two processing branches are combined again by addition.
In digital technology, the formation of the radio-frequency component can be performed by the video signal being delayed by one pixel, one line or one frame and the delayed signal being subtracted from the undelayed signal. In this way, the relation with respect to the neighboring signal values is established. A radio-frequency signal which can be further processed is produced only if the neighboring, delayed signal value is changed with respect to the undelayed signal value. By this technique it is possible to amplify worn signal details and thus achieve an improvement in the picture quality with regard to the signal details. It is likewise known from Lebowsky, "Hierarchische Bildqualitatsverbesserung mit Multiprozessorsystemen" (Hierarchical Picture Quality Improvement with Multiprocessor Systems), Fernseh- und Kino-Technik (Television and Cinema Technology) 1992, pages 155 to 164, incorporated herein by reference, to filter out from the luminance signal a detail signal by a two-dimensional high-pass filter and feed it to a coring stage, which suppresses low amplitudes of the filtered-out signal and linearly amplifies amplitudes lying above a threshold value. Owing to established disadvantages of this method, a gradient-oriented method with a filter bank with anisotropic filters of differing orientation has also been utilized. This method, like the method described above, has advantages and disadvantages.